1.7 Feature List

The Crystal Entity Layer provides higher-level ways to control objects than
you'd have by using Crystal Space alone. It also provides features not
present in Crystal Space, therefore saving you a lot of time you'd spend
implementing them yourself.

Entity system

Entities provide a convenient way to access and control objects' features and
properties. Entities are not required to have a visual representation.
One simply adds features to an entity by attaching property classes, then
handling the messages this entity receives.

Scripting

CEL has Python bindings, and its own XML-based script language.
You can use either of those, on a per-entity basis.
Using CELStart, you can build an application without any line of C++.
Indeed, you can also use them from your own C++ code.